1. Field of the Invention
The invention relates to a control technique for DC-to-AC converters, and in particular to a method for controlling operation of DC-to-AC converters which operates for bipolar output, automatically compensates switching errors and excluding unstable operating conditions to overcome the inherent nonlinearity of switching power amplifiers, eliminating crossover distortion, rejecting power source ripple and achieving a broad dynamic range and wide bandwidth.
2. Description of the Prior Art
To date, most commercially available audio power amplifiers are configure to operate linearly. Therefore, they suffer from low efficiency and have a bulky volume. Conventional switching converters provide a high efficiency and low volume alternative for audio power amplification, but in turn, suffer from a low signal-to-noise ratio due to their inherent nonlinearity and crossover distortion.
One cycle control has been successfully used in DC-to-DC converters and has proven to have many advantages over other control methods. See K. Smedley et al., "One-Cycle Control of Switching Converters," PESC Record 1991 at 1173-80 (IEEE Publication 92ch3163-3) and Smedley, "One Cycle Controlled Switching Circuit," U.S. Pat. No. 5,278,490 (1994). This control technique uses an integration and reset method to force the switched variable to be exactly equal to the control reference in each switching cycle, regardless of the power source ripple and the switching error. It decouples the input and output stages of converter. Therefore, the system order is reduced, the perturbation from input stage to output stage is rejected, and the system dynamic response is very fast. The nonlinear switching converter behaves like a linear system. The generality of this control method has been confirmed by applying it to all types of DC-to-DC pulse width modulated or quasi-resonant converters for either voltage or current control.
However, what is needed is an extension of the one cycle control for DC-to-AC conversion with special attention to the specific requirements of audio power amplification.